Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of determining an uplink transmission timing of a user equipment (UE) having a plurality of cells configured therefor.
Related Art
Long Term Evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (2009 May) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, in LTE, a physical channel can be divided into a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH), that is, downlink channels, and a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUSCH), that is, uplink channels.
A PUCCH is an uplink control channel used to send uplink control information, such as a Hybrid Automatic Repeat reQuest (HARQ), an acknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel Quality Indicator (CQI), and a Scheduling Request (SR). Currently, 3GPP LTE-Advanced (LTE-A) as an evolved version of 3GPP LTE is progressing.
Meanwhile, a conventional wireless communication system uses either of time division duplex (TDD) and frequency division duplex (FDD). TDD is a technique where the same frequency band is used for an uplink and a downlink at different times. FDD is a technique where different frequency bands are used for an uplink and a downlink. FDD uses two different frequency bands to allow uplink and downlink transmissions simultaneously, whereas TDD does not allow simultaneous uplink and downlink transmissions.
When FDD is used, in which a downlink and an uplink use the same frequency band, resources are allocated to the downlink and the uplink at a fixed ratio of 1:1. However, when data traffic is concentrated in either of the downlink and the uplink, the resources may not be efficiently used.
FDD needs new communication methods. When an advanced user equipment (UE) using a new communication method coexists with a conventional UE, communication standards based on the conventional FDD technique need to be changed.
Meanwhile, two cells may be configured for a UE. For example, an FDD cell using FDD and a TDD cell using TDD may be configured for a UE. A timing advance (TA) value, which indicates how much earlier a conventional uplink radio frame is transmitted than a downlink radio frame, is determined on a duplexing mode used in a cell on the assumption that cells using the same duplexing mode are aggregated for one UE.
Thus, it is necessary to modify a conventional TA determination method for a wireless communication system in which cells using different duplexing modes may be aggregated.